The present invention relates to a small camera having a separate photographing optical system and finder optical system. More particularly, this type of small camera utilizes the so-called phase difference detecting method for detecting a focus point, generally employed in a single-lens refrex camera.
The compact camera described above was the first camera provided with an automatic focusing mechanism because the mechanism was relatively uncomplicated. This was so because a photographing lens of the camera is not much different from that of a single-lens reflex camera and the focusing accuracy required for the camera is not so high as that required in the single-lens reflex camera.
Conventionally, compact cameras employ a distance detecting device making use of the principle of triangulation because it does not require a high focusing accuracy and as the camera has a small body the automatic focusing mechanism must be compact.
Today, however, as the function of the compact camera becoming more sophisticated, a more accurate focusing mechanism is required then in the past. The problem is whether a phase difference detecting method is applicable to the compact camera or not, since methods employed by single-lens reflex cameras which requires a higher degree of accuracy.
In general, a detecting element of a focusing device employed in the single-lens reflex camera is an image surface processing type device disposed at a position conjugate with an image surface. When this image surface processing type element is disposed in front of the image surface, a distance between the element and an image is increased, and thus the size of a sensor itself is increased. Accordingly an aberrations must increasingly be corrected; and the light receiving element must be disposed behind a film equivalent surface. With the single-lens reflex camera, this element may be disposed behind the image surface, because this camera has a relatively large body and a light passage can be diverted by a quick return mirror interposed between a photographing lens and a film.
This arrangement, however, cannot be employed in the compact camera because no space is available for the element.